The present invention relates to over-voltage protection circuits. More particularly, the present invention relates to over-voltage protection circuits having metal oxide varistor (MOV) devices as the over-voltage sensing component. Even more particularly, the present invention relates to over-voltage protection circuits having metal oxide varistor (MOV) devices as the over-voltage sensing component for utilization in AC electric power distribution.
The current state of the art electronic components (e.g., both commercial and residential computers and related equipment) accommodate transient voltage surge suppression features for protecting their highly sensitive circuits from over-voltage damage. Most transient voltage surge suppression systems today address only minor fault conditions associated with normal use and cannot handle a major over-voltage condition as would occur during loss of neutral, loss of ground, or repetitive current pulses (e.g., from a lightning strike). Typical voltage surge protection devices comprise either a plurality of fault fuses where the input is disconnected from the output. The related art surge suppression systems may involve various metal oxide varistor (MOV) and fuse combinations. MOVs are typically non-linear devices formed from composite ceramic materials (e.g., ZnO grains in combination with an amorphous material). MOVs maintain the voltage within a narrow band (i.e., varistor voltage) over a wide current range. During major over-voltage conditions, the MOVs may absorb heat so excessive such that they will rupture or explode, thereby allowing the related electronic equipment to be destroyed.
Some related art surge suppression apparatus patents include:
(1) U.S. Pat. No. 6,055,147 to Jeffries et al. which teaches a plurality of MOVs being in series with a plurality of thermal fuses;
(2) U.S. Pat. No. 5,412,526 to Kapp et al. which teaches a plurality of MOVs being in series with a plurality of thermal fuses, and the plurality of MOVs being in parallel with a plurality of resistors;
(3) U.S. Pat. No. 6,040,971 to Martenson et al. which teaches a plurality of MOVs being in parallel with one another, an MOV being in parallel with a thermal fuse, and the thermal fuse being in series with a circuit protection device having an over-voltage trip device;
(4) U.S. Pat. No. 5,388,021 to Stahl which teaches a plurality of MOVs being in parallel with a plurality of resistors and a plurality of inductors, and a plurality of MOVs being in parallel with another;
(5) U.S. Pat. No. 5,675,468 to Chang which teaches two input terminals, two fuses in series respectively, a triac, an MOV in series between one fuse and an output terminal, a static potential limiter between the triac and ground;
(6) U.S. Pat. No. 4,901,183 to Lee which teaches two MOVs being in parallel with one another, two thermal fuses being in parallel with one another, a capacitor being in parallel with an MOV, two capacitors being in parallel with one another, and two inductors being in parallel with one another;
(7) U.S. Pat. No. 6,038,117 to Dullni et al. which teaches pairs of MOVs being in parallel, a plurality of such pairs being in series with one another and in series with a relay;
(8) U.S. Pat. No. 5,534,769 to Ishii which teaches resistor-capacitor combinations; and
(9) U.S. Pat. No. 5,808,850 to Carpenter, Jr. which teaches a three-phase device having quadruplets of parallel MOVs, each quadruplet being in series with a thermal fuse and an inductor, and bulbs for an indicator light for line to ground only.
A typical problem associated with these related art inventions is that an electrician may accidentally reverse the line wire and the neutral wire, creating an extremely hazardous situation at the wall receptacle, even if the invention succeeds in disconnecting the circuit to a peripheral device. In addition, the related art patents maintain an inordinately high component count to achieve their purpose of surge suppression. Therefore, a need exists for a circuit apparatus and a method which prevent (1) the hazardous condition occurring at the wall receptacle, arising from accidental reversal of the line wire with the neutral wire, from adversely affecting at least one peripheral device in the line, and (2) the overheating and destruction of MOVs in an over-voltage protection circuit by providing an efficient circuit configuration (i.e., the minimum number of components for device size reduction) which assures a rapid simultaneous disconnect of both the hot line and the neutral line.
An object of the present invention is to provide an apparatus and a method which prevent (1) the hazardous condition occurring at the wall receptacle, arising from accidental reversal of the line wire with the neutral wire, from adversely affecting at least one peripheral device in the line, and (2) the overheating and destruction of MOVs in an over-voltage protection circuit by providing an efficient circuit configuration (i.e., the minimum number of components for device size reduction) which assures a rapid simultaneous disconnect of both the hot line and neutral power lines.
Another object of the present invention is to provide an apparatus and a method which prevent (1) the hazardous condition occurring at the wall receptacle, arising from accidental reversal of the line wire with the neutral wire, from adversely affecting at least one peripheral device in the line, and (2) the overheating and destruction of MOVs in an over-voltage protection circuit by opening the circuit to simultaneously disconnect both the hot line and the neutral line feeding a load when the over-voltage event occurs in any of three wire pairings: line-to-neutral (L-N), line-to-ground (L-G), or neutral-to-ground (N-G).
Accordingly, the present invention provides a single-phase over-voltage protection circuit apparatus for all AC power lines and combinations thereof. In particular, the present invention provides an apparatus and a method which prevent (1) the hazardous condition occurring at the wall receptacle, arising from accidental reversal of the line wire with the neutral wire, from adversely affecting at least one peripheral device in the line, and (2) the overheating and destruction of MOVs in an over-voltage protection circuit by providing an efficient circuit configuration which assures a rapid simultaneous disconnect of both the hot line and neutral line. The present invention achieves this by opening the circuit to simultaneously disconnect both hot line and neutral line feeding a load when the over-voltage event occurs in any of the three following wire pairings: hot line to neutral line (L-N), hot line to ground line (L-G), or neutral line to-ground line (N-G).
By example, in a single phase AC power system, the hot line (L), the neutral line (N), and ground line (G) are all paths vulnerable to destructive high voltages. The present invention protects these paths by first providing protection devices in the form of metal oxide varistors (MOVs) in parallel for each pair of wires (i.e., hot line to neutral, hot line to ground, and neutral to ground). The apparatus additionally comprises in-line fuses and a normally open relay device that disconnects both the hot line as well as the neutral line from the load. The MOV devices are activated by an over-voltage condition and upon absorbing all the extra and potentially damaging power surges and over-voltages which cause excessive current to flow, which then opens the fuse, causing de-energizing of the relay device.
Accordingly, in the event of a sufficiently high voltage (i.e., VL-N greater than 120 V to 130 V), from hot line-to-neutral or hot line-to-ground, causing excessive heating of the MOV protection devices, the hot line and neutral line will be disconnected from the user""s connected equipment. This disconnect is facilitated by the use of an open circuit condition of the in-line special fuses which causes de-energizing of the relay device and reversion of the relay contacts back to a normally open condition. Preferably, this is a non-resettable disconnect condition that maintains the relay in its normally open condition, especially where the over-voltage protection circuit is the final protection to the connected equipment for preventing excessive current and heating which, otherwise, would lead to smoke and/or fire. In the preferred embodiment, the relay simultaneously disconnects the hot line as well as the neutral line from the connected peripheral equipment (i.e., the load) such as audio and visual devices.
The current through the line may be denoted by IL. The current through an MOV, IMOV, must remain less than the rated current for the MOV, IMOV-rated, in normal operation. During an over-voltage event where the current through the MOV exceeds its current rating (i.e., IMOV greater than IMOV-rated), thereby effecting a current through the thermal fuse exceeds its current rating (IL=ITF, ITF greater than ITF-rated), such thermal fuse will open, thereby preventing voltage application to the relay, thereby preventing the relay from being energized, and thereby effecting its normally-open contact state (See FIG. 1).
In all the foregoing protection modes (i.e., L-N, L-G, N-G), a warning feature may be provided which indicates that a protection device (e.g., an MOV) has absorbed an excessive energy, thereby opening a thermal fuse which effectively opens the path to any protection device and to the load. The warning feature may continue to alert the user even if power is no longer applied to the equipment. This warning feature alerts the user of the otherwise potentially destructive event. Upon so alerting the user, the apparatus should be unplugged from the wall outlet and the thermal fuse replaced. This warning feature may be audio and/or visual in nature.
Other features of the present invention are disclosed, or are apparent in the section entitled xe2x80x9cDETAILED DESCRIPTION OF THE INVENTION.xe2x80x9d